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Lathe spindle box and rest
Of the many standard and special types of turning machines that have been built, the most important, most versatile and most widely recognized is the engine lathe. The standard engine lathe is not a high production machine, but it can be readily tooled up for many one-piece or short-run jobs. It is also possible to modify the basic machine for many higher production applications. The modern engine lathe provides a wide range of speeds and feeds which allow optimum setting for almost any operation. There have been advances in headstock design to provide greater strength and rigidity. This allow the use of high–horsepower motors so that heavy cuts with carbide tools are practical. To utilize this high power without losing accuracy, new lathes incorporate heavier beds, wider hardened ways and deeper-sectioned carriages.
Headstock: The headstock is the powered end and is always at the operator’s left. This contains the speed changing gears and the revolving, driving spindle, to which any one of several types of work holders is attached. The center of the spindle is hollow so that long bars may be put through it for machining.
The headstock incorporates the driving and gear mechanism, and a spindle which holds the work piece and cause it to rotate at a speed which depends largely on the diameter of the work piece. A bar of large diameter should naturally rotate more slowly than a very thin bar, the cutting speed of the tool is what matters. Tapered centres in the hollow nose of the spindle and of the tailstock hold the work firmly between them. A feed-shaft from the headstock drives the tool-post along the saddle, either forwards or backwards, at fixed and uniform speed. This enables the operator to make accurate cuts and to give the work a good finish. Gears between the spindle and the feed-shaft control the speed of rotation of the shaft, and therefore the forward or backward movement of the tool-post. The gear which the operator will select depends on the type of the metal which he is cutting and the amount of metal he has to cut off. For a deep or roughing cut the forward movement of the tool should be less than for a finishing cut.
Centres are not suitable for every job on the lathe. The operator can replace them by various types of chucks, which hold the work between jaws, or by a front-plate, depending on the shape of the work and the particular, cutting operation. He will use a chuck, for example, to hold a short piece of work, or work for drilling, boring or screw-cutting. A transverse movement of the tool-post across the saddle enables the tool to cut across the face of the work piece and give it a flat surface. For screw-cutting, the operator engages the lead screw, a long screwed shaft which runs along in front of the bed and which rotates with the spindle. The lead-screw drives the tool-post forwards along the carriage at the correct speed, and this ensures that threads on the screw are of exactly the right pitch. The operator can select different gear speeds, and this will alter the ratio of spindle and lead screw speeds and therefore alter the pitch of the threads. A reversing lever on the headstock enables him to reverse the movement of the carriage and so bring the tool back to its original position.
Compound Rest: The compound rest, or compound for short, is mounted on the carriage. It can be moved in and out by its handwheel for facing or for setting the depth of cut. It can also be rotated 360 degrees and fed by its handwheel at any angle. The compound does not have any power feed but it always moves longitudinally with the cross slide and the carriage.
Tool Post: The tool post is mounted on the compound rest. This can be any of several varieties but in its simplest form is merely a slotted cylinder which can be moved left or right in the T-slot in the compound and clamped in place. It can also be rotated so as to present the cutter to the work at whatever angle is best for the job
A lathe holds the work piece and rotates it, and the sharpened edge of a tool cuts and removes material. Some applications of a lathe include the production of shafts, and thread cutting. The chuck on headstock hold one end of a work piece, and the drive mechanism spins it rapidly about its centerline. The tailstock can be used to provide support to the otherwise free end of a long work piece. As a cutting tool is fed against the bar stock and moved along its length, the diameter of the work piece is reduced to a desired dimension, Shoulder that will locate bearings on a shaft, grooves for holding retaining clips, and sharp changes in diameter of a stepped shaft cam each be made in this manner.
Key word: The spindle box Gear mechanism Rest